U.S. patent number 5,199,859 [Application Number 07/701,890] was granted by the patent office on 1993-04-06 for refrigerant compressor.
This patent grant is currently assigned to Kabushiki Kaisha Toshiba. Invention is credited to Shoichiro Kitaichi.
United States Patent |
5,199,859 |
Kitaichi |
April 6, 1993 |
Refrigerant compressor
Abstract
A compressing mechanism includes a slidable section which is
constructed by combining a first slidable member made of a cast
iron having a Vickers hardness within the range of 200 to 300 with
a second slidable member made of a carbon steel having a Vickers
hardness within the range of 200 to 300 and an average number of
crystalline grains per 1 mm.sup.2 within the range of 2000 to 3200.
The slidable section is composed of a shaft and a bearing.
Additionally, the slidable section includes a cylinder, a rotor and
a piston. Each crystalline grain in the carbon steel constituting
the second slidable member has a substantially isotropic shape and
a size of the crystalline grain is suitably enlarged to exhibit a
coarse structure. As a result, elasticity of the grain structure of
the carbon steel is increased and a very small number of
crystalline grains are peeled off from the surface of the
substrate. Since the slidable section is constructed by combining
the first slidable member with the second slidable member in the
above-described manner, the second slidable member exhibits
excellent wear resistance even under a circumstance wherein the
1,1,1,2-tetrafluoroethane or the 1,1-difluoroethane is used as a
refrigerant in the presence of a polyether-based oil, a
polyester-based oil or the like each serving as a refrigerator
oil.
Inventors: |
Kitaichi; Shoichiro (Kanagawa,
JP) |
Assignee: |
Kabushiki Kaisha Toshiba
(Kanagawa, JP)
|
Family
ID: |
14964099 |
Appl.
No.: |
07/701,890 |
Filed: |
May 17, 1991 |
Foreign Application Priority Data
|
|
|
|
|
May 17, 1990 [JP] |
|
|
2-127600 |
|
Current U.S.
Class: |
417/410.1;
418/179 |
Current CPC
Class: |
F04C
23/008 (20130101); F04C 29/02 (20130101); F04C
2210/26 (20130101); F05B 2210/14 (20130101); F05C
2201/0448 (20130101); F05C 2251/02 (20130101); F05C
2253/08 (20130101) |
Current International
Class: |
F04C
29/02 (20060101); F04C 23/00 (20060101); F04B
039/12 (); F04C 029/02 () |
Field of
Search: |
;418/179 ;384/912
;417/410 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
450847 |
|
Dec 1991 |
|
EP |
|
300084 |
|
Dec 1989 |
|
JP |
|
Other References
Preprint of the 34th Journal of Japan Society of Lubrication
Engineers Conference, Y. Honma et al., 1989..
|
Primary Examiner: Smith; Leonard E.
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt
Claims
What is claimed as new and desired to be Secured by Letters Patent
of the United States is:
1. A refrigerant compressor in which 1,1,1,2-tetrafluoroethane or
1,1-difluoroethane is used as the refrigerant, comprising:
a closed casing in which said refrigerant and a refrigerator oil
having compatibility with said refrigerant are received,
a compressing mechanism including a slidable section constructed by
combining a first slidable member made of a cast iron having a
Vickers hardness within the range of 200 to 300 with a second
slidable member made of a carbon steel having a Vickers hardness
within the range of 200 to 300 and an average number of crystalline
grains per 1 mm.sup.2 within the range of 2000 to 3200, said
compressing mechanism being accommodated in said closed casing,
and
a motor mechanism for driving said compressing mechanism.
2. The refrigerant compressor as claimed in claim 1, wherein said
slidable section includes a shaft for transmitting to said
compressing mechanism a driving force generated by said motor
mechanism and a bearing for rotatably supporting said shaft.
3. The refrigerant compressor as claimed in claim 2, wherein said
shaft is constituted by said first slidable member and said bearing
is constituted by said second slidable member.
4. The refrigerant compressor as claimed in claim 1, wherein said
refrigerator oil includes at least one kind of oil selected from an
ether-based oil, an ester-based oil and a fluorine-based oil.
5. The refrigerant compressor as claimed in claim 1, wherein said
carbon steel includes crystalline grains each having a
substantially isotropic shape.
6. The refrigerant compressor as claimed in claim 1, wherein said
slidable section includes a cylinder and a movable member for
compressing said refrigerant while coming in slidable contact with
the inner wall surface of said cylinder.
7. The refrigerant compressor as claimed in claim 6, wherein said
cylinder is constituted by said first slidable member and said
movable member is constituted by said second slidable member.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention:
The present invention relates generally to a compressor for
compressing a refrigerant. More particularly, the present invention
relates to a refrigerant compressor in which
1,1,1,2-tetrafluoroethane or 1,1-difluoroethane is employed as the
refrigerant.
2. Description of the related art:
Generally, a refrigerant compressor is used for an air conditioner,
a refrigerator or the like so as to blow cool air or warm air into
the interior of a room, a vehicle's cabin or the like. A hermetic
refrigerant compressor and a semihermetic refrigerant compressor
have been hitherto known as the refrigerant compressor, for a car
air conditioner.
For example, the hermetic refrigerant rotary compressor includes a
motor mechanism and a compressing mechanism which are arranged in a
casing. The motor mechanism is operatively connected to the
compressing mechanism via a shaft so that the compressing mechanism
is driven by the motor mechanism via the shaft.
The compressing mechanism may, for example, include a cylinder and
a roller eccentrically fixedly mounted on the shaft which is
rotatably disposed in the cylinder. In addition, the compressing
mechanism includes a blade which is protruded through the cylinder.
One end of the blade is brought in slidable contact with the outer
surface of the roller by the resilient force of a spring. The blade
serves to divide the interior of the cylinder into a suction
chamber and a discharge chamber. As the shaft is rotated, the
roller repeatedly performs planetary movement to compress a
refrigerant. The refrigerant which has been compressed is first
discharged into the casing, and thereafter it is delivered to a
refrigerator via a discharge tube. Slidable members such as a
roller, a blade and so forth are constructed such that they
smoothly move in the presence of a refrigerator oil which is
received and stored in the casing. Things are the same with the
shaft.
Dichloromethane (hereinafter referred to as CFC 12) and
chlorodifluoromethane (hereinafter referred to as HCFC 22) have
been mainly employed as the refrigerant in the refrigerant
compressor. Further, a naphthene-based mineral oil and a
paraffin-based oil each having solubility relative to the CFC 12
and the HCFC 22 have been employed as the refrigerator oil to be
received in the compressing mechanism.
In recent years, it has been clarified that a flon discharged from
each of the aforementioned refrigerants has serious effects on
human beings as well as animals and plants. For this reason, it has
been determined, on a global base, that employment of the CFC 12
and others, each having a high ozone depletion potential, is to be
reduced year by year and employment of the aforementioned
refrigerants will be prohibited in the future. In view of the
foregoing circumstances, 1,1,1,2-tetrafluoroethane (hereinafter
referred to as HFC 134a), 1,1-difluoroethane (hereinafter referred
to as HFC 152a) and the like have been developed to be substituted
for the CFC 12. In practice, the HFC 134a, the HFC 152a and the
like have a low ozone depletion potential, respectively. However,
they are hardly dissolved in the mineral oil which has heretofore
been used as the refrigerator oil. For this reason, endeavors have
been made to use a polyether-based oil, a polyester-based oil, a
fluorine-based oil or the like, each having compatibility with HFC
134a and the HFC 152a when they are used as a refrigerant.
However, in the case where the HFC 134a or the HFC 152a is used as
a refrigerant, to be substituted for the CFC 12 and, e.g., a
polyether-based oil or a polyester-based oil is used as the
refrigerator oil having solubility relative to the foregoing
refrigerant, there arises a problem in that slidable members in the
compressing mechanism or the like in the refrigerant compressor are
greatly worn as the refrigerant compressor is operated. This
problem leads to the result that the refrigerant compressor can not
be stably operated for a long time.
Components in the refrigerant compressor which will be worn are
classified into two groups, one of them being the shaft and
associated components, and the other one being the blade, the
roller (or the piston) and associated components. The shaft is
rotated at a high rotational speed while it receives a spring force
and a pressure in the cylinder via a roller and thereby it is
slightly bent or curved due to slidable contact with a frame and a
bearing, each serving to rotatably support the shaft. Consequently,
the outer surface of the shaft and the inner surface of the bearing
are unavoidably worn as the refrigerant compressor is driven. On
the other hand, the blade rubs against the inner surface of a
through aperture formed in the cylinder, due to the differential
pressure between the two divided chambers in the cylinder, causing
both the blade and the cylinder to be worn. In addition, since the
foremost end of the blade is normally squeezed against the roller
by the resilient force of the spring, the outer surface of the
roller is worn too.
To fabricate slidable members such as a shaft or the like, a cast
iron (e.g., JIS FC 25 specified in accordance with Japanese
Industrial Standard (hereinafter referred to simply as FC 25)), a
carbon steel (e.g., S12C, S15C or the like), a carbon steel for
cold heading and cold forging (e.g., SWRCH 10A, SWCH 15A or the
like), a carbon steel for machine structural use (SCM 435H or the
like), a stainless steel, a sintered alloy and similar metallic
materials have heretofore been used. However, it has been found
that the carbon steel and others are greatly worn as the
refrigerant compressor is operated with the use of the refrigerant
and the refrigerator oil as mentioned above. Once the slidable
members in the refrigerant compressor are worn, the ability to
compress the refrigerant is degraded. As a result, it becomes
difficult to operate the refrigerant compressor properly.
It is considered that wear of the slidable members is caused for
the following reasons.
Specifically, in the case where CFC 12 is used as refrigerant,
chlorine atoms in the CFC 12 react with iron atoms in each slidable
member to thereby form a film of iron chloride having excellent
wear resistance. In contrast with the CFC 12, in the case where HFC
134a is used as the refrigerant, since the HFC 134a contains no
chlorine atom, a film of lubricant, such as the film of iron
chloride, is not formed due to the absence of chlorine atoms,
resulting in the lubricating function being deteriorated. On the
other hand, since a conventional mineral oil-based refrigerator oil
contains a cyclic compound, it has a comparatively high ability of
forming an oil film. On the contrary, since the refrigerator oil
having compatibility with HFC 134a or HFC 152a is composed of a
cyclic compound as a main substance, it can not maintain an oil
film having a certain adequate thickness under severe slidable
conditions.
A carbon steel widely used as a material for slidable members is
normally plastically processed in the form of a cold heading and
has a Vickers hardness within the range of 300 to 500. After
completion of the cold heading, the carbon steel has work hardness
and exhibits a cold-rolled structure in which crystalline grains
are elongated in the direction of working. FIG. 10 is a microscopic
photograph which illustrates a macrostructure of the cold-rolled
structure of the carbon steel on the surface of a cut piece thereof
(refer to page 38 in the Section on steel materials in Collection
Of Microscopic Photographs, 1979 edition, each illustrating a
macrostructure of each of the steel material, edited by the Japan
Metallic Material Association). In FIG. 10, the crystalline grains
elongating in the direction of rolling with a white color represent
a ferrite, and the crystalline grains remaining between the white
crystalline grains while exhibiting a black color represent a
perlite, respectively. Since the carbon steel having the
aforementioned grain structure is forcibly pulled during a rolling
operation, a residual stress remains within the carbon steel,
causing the carbon steel to be kept in the thermally unstable
state.
Therefore, the surface structure of a slidable member fabricated by
using the carbon steel kept in the thermally unstable state is
readily peeled off from the surface of the substrate for the
above-described reasons, unless a film of lubricant is
satisfactorily formed on the surface of the substrate of the carbon
steel. Once peeling has occurred, grains peeled off therefrom act
as burrs and scrape the surface of opposed slidable members. As a
result, the wear loss of the carbon steel is increased.
In addition, HFC 134a, HFC 152a and the refrigerator oils
compatible with them have high moisture absorbability. Since the
refrigerant and the refrigerator oil normally recirculate through
the casing, a film of lubricant on the surface of each slidable
member is decomposed as the quantity of water in the refrigerant
and the refrigerator oil increases. As a result, corrosive wear
occurs with the slidable members. Indeed, the corrosive wear
proceeds at an accelerated speed. Consequently, reduction of wear
resistance of the slidable members is promoted.
Therefore, many requests have been received from users for
improving wear resistance of the slidable members in the
refrigerant compressor when HFC 134a or HFC 152a are employed as a
new refrigerant, to be substituted for CFC 12, and a refrigerator
oil having compatibility with the foregoing refrigerants are used
in the refrigerant compressor. In addition, another important
subject is to make it possible to operate the compressor for a long
time by improving wear resistance of the slidable members.
SUMMARY OF THE INVENTION
The present invention has been made with the foregoing background
in mind.
An object of the present invention is to provide a refrigerant
compressor which makes it possible to stably operate the compressor
for a long time by improving wear resistance of each of slidable
members used to constitute a slidable section while
1,1,1,2-tetrafluoroethane or 1,1-difluoroethane is used as the
refrigerant.
Another object of the present invention is to provide a method of
fabricating a slidable member for a refrigerant compressor in which
1,1,1,2-tetrafluoroethane or 1,1-difluoroethane is used as the
refrigerant while each slidable member is made of a carbon
steel.
To accomplish the former object, the present invention provides a
refrigerant compressor in which 1,1,1,2-tetrafluoroethane or
1,1-difluoroethane is used as the refrigerant, wherein the
compressor includes a closed casing in which the refrigerant and a
refrigerator oil having compatibility with the refrigerant are
received, a compressing mechanism including a slidable section
constructed by combining a first slidable member made of a cast
iron having a Vickers hardness within the range of 200 to 300 with
a second slidable member made of a carbon steel having a Vickers
hardness within the range of 200 to 300 and an average number of
crystalline grains per 1 mm.sup.2 within the range of 2000 to 3200,
the compressing mechanism being accommodated in the closed casing,
and a motor mechanism for driving the compressing mechanism.
Since the slidable section in the compressing mechanism is
constructed by combining the first slidable member with the second
slidable member, a resistive force against heat generated by
friction in the slidable section can substantially be enlarged even
when a film of lubricant fails to be formed due to the presence of
chlorine atoms or the oil film retaining power of a refrigerator
oil is reduced undesirably.
Further, to accomplish the latter object, the present invention
provides a method of fabricating a slidable member for a
refrigerant compressor in which 1,1,1,2-tetrafluoroethane or
1,1-difluoroethane is used as the refrigerant, the slidable member
being made of a carbon steel wherein the method includes a step of
machining the carbon steel to assume a required configuration, a
step of allowing the carbon steel which has been machined to the
required configuration to be subjected to heat treatment at a
temperature corresponding to a carbon content of the carbon steel
so as to transform a grain structure of the carbon steel into a
uniform austenite structure, and a step of gradually cooling the
carbon steel after completion of the heat treatment so as to adjust
the Vickers hardness of the carbon steel to remain within the range
of 200 to 300 and adjust the average number of crystalline grains
per 1 mm.sup.2 to remain within the range of 2000 to 3200.
Other objects, features and advantages of the present invention
will become apparent from reading the following description which
has been made in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention is illustrated in the attached drawings in
which:
FIG. 1 is a vertical sectional view of a refrigerant compressor in
accordance with an embodiment of the present invention;
FIG. 2 is a cross-sectional view of a compressing mechanism in the
compressor in FIG. 2;
FIGS. 3(a) and 3(b) shows microscopic photographs each of which
illustrates a macrostructure of a carbon steel employed for a
bearing in the refrigerant compressor in accordance with an
embodiment of the present invention;
FIGS. 4(a) and 4(b) shows microscopic photographs each of which
illustrates a macrostructure of a carbon steel for a bearing in a
refrigerant compressor in accordance with another embodiment of the
present invention;
FIGS. 5(a) and 5(b) shows microscopic photographs each of which
illustrates a macrostructure of a carbon steel for a bearing in a
conventional refrigerant compressor;
FIG. 6 is a schematic sectional view of a wear testing machine
which is used for testing wear resistance of a shaft arranged in
the refrigerant compressor of the present invention;
FIG. 7 is a diagram which illustrates a relationship between the
Vickers hardness of a carbon steel and the quantity of wear of the
carbon steel;
FIG. 8 is a diagram which illustrates a relationship between the
number of crystalline grains in a carbon steel and the quantity of
wear of the carbon steel;
FIG. 9 is a graph which illustrates the quantity of wear of
slidable members to be combined with each other, with respect to
Examples 1 to 4, Comparative Examples 1 and 2 and the Reference
Example;
FIG. 10 is a microscopic photograph which illustrates a
macrostructure of a cold-rolled ordinary carbon steel;
FIG. 11 is a table which illustrates moisture absorbability of
various kinds of lubricants; and
FIG. 12 is a diagram which illustrates water-solubility of various
kinds of refrigerants.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Now, the present invention will be described in detail hereinafter
with reference to the accompanying drawings which illustrate a
preferred embodiment of the present invention.
FIG. 1 is a sectional view of a rotary-type refrigerant compressor
in accordance with an embodiment of the present invention.
In the drawing, reference numeral 11 designates a closed casing. A
motor mechanism 17 comprising a stator 13 and a rotor 15 is
accommodated in the hermetic casing 11. In addition, a compressing
mechanism 19 is arranged in the region below the motor mechanism 17
as seen in the drawing. The motor mechanism 17 and the compressing
mechanism 19 are operatively connected to each other via a shaft
21. As a driving force is generated by the motor mechanism 17, it
is transmitted to the compressing mechanism 19 via the shaft 21 to
drive the compressing mechanism 19.
As the compressing mechanism 19 is driven, the refrigerant which
has been introduced into the compressor via an accumulator (not
shown) and a refrigerant supply tube 23 is compressed by the
compressing mechanism 19. The compressed refrigerant is first
delivered to the interior of the casing 11, and thereafter the
compressed refrigerant is supplied to a refrigerator (not shown)
via a discharge tube 25 which is fixedly fitted to the upper end of
the casing 11.
To operate the compressor, 1,1,1,2-tetrafluoroethane (hereinafter
referred to as a HFC 134a) or 1,1-difluoroethane (hereinafter
referred to as a HFC 152a) is used as refrigerant. Since both
refrigerants contain no chlorine atom, the ozone depletion
potential of each of the refrigerants is zero. For this reason,
they are preferably employed, from the viewpoint of protection of
the environment. Although HFC 134a does not have a high energy
efficiency, it has the advantage that a refrigerating system
associated with the refrigerant compressor of the present invention
can be replaced with the current refrigerating system. In addition,
although HFC 152a is inflammable, it has the advantage that it has
a very high energy efficiency.
The compressing mechanism 19 will be described in more details
below with reference to FIG. 2.
The shaft 21, adapted to be rotated by the motor mechanism 17, is
rotatably supported by a bearing fitted into a frame 27, and the
lower end part of the shaft 21 is rotatably supported by a
subbearing 29. The shaft 21 is arranged to extend through a
cylinder 31. A crank portion 33 in the form of an eccentric is
fixedly mounted on a part of the shaft 21 in the cylinder 31 and a
roller 35 is fitted onto the crank portion 33 in the space between
the crank portion 33 and the cylinder 31. As the shaft 21 is
rotated, the roller 35 repeatedly performs planetary movement.
A movable blade 37 is protruded into the cylinder 31. The blade 37
is arranged in a through aperture 31a which is formed in the
cylinder 31 so that the biasing force of a spring 39 is imparted to
the blade 37. As the roller 35 performs planetary movement, the
blade 37 moves reciprocably. One end of the blade, i.e., the
right-hand end of the blade 37 as seen in FIG. 2 comes in slidable
contact with the outer peripheral surface of the roller 35 while
dividing the interior of the cylinder 31 into a suction chamber 41
and a discharge chamber 43. In response to planetary movement of
the roller 35 caused as the shaft 21 is rotated, the refrigerant is
sucked into the compressor via a suction port 45 so that it is
compressed by the compressor.
A refrigerator oil 47 is received and reserved in the lower part of
the casing 11. As the shaft 21 is rotated, the refrigerator oil 47
is sucked up by a pump (not shown) disposed at the lower end of the
shaft 21 so as to lubricate slidable portions in the
compressor.
It is required that a refrigerator oil having compatibility with
the HFC 134a or the HFC 152a serving as a refrigerant is used so as
to properly utilize the refrigerator oil 47 in the casing 11. This
is because the refrigerator oil should reliably be returned to the
compressor during a refrigerating cycle while preventing the
refrigerator oil from remaining in the refrigerator. An ether-based
oil, an ester-based oil, a fluorine-based oil or the like can be
noted as a refrigerator oil having compatibility with HFC 134a and
with HFC 152a. Among the aforementioned refrigerator oils, a
polyalkylane glycol-based oil that is a kind of ether-based oil is
preferably employable for HFC 134a and HFC 152a, because it has
excellent properties of high viscosity and low flowability. It
should be added that the ester-based oil is superior in respect of
low moisture absorbability. Additionally, a mixture of the
ether-based oil, a naphthene-based mineral oil, a paraffin-based
mineral oil and an alkylbenzene may be employed.
The slidable portions in the compressor in accordance with the
embodiment of the present invention, i.e., the slidable portions to
be lubricated with one of the aforementioned refrigerator oils,
will be noted below.
Since the shaft 21 receives the resilient force of the spring 38
and the pressure appearing in the cylinder 31, it is normally
biased to come in close contact with the frame 27 and the
subbearing 29, causing the shaft 21 to be rotated at a high
rotational speed in the slightly bent or curved state. Therefore,
the contact portions at which the outer surface of the shaft 21
comes in contact with the inner surfaces of the frame 27 and the
subbearing 29 become a slidable portion, respectively. As the shaft
21 is rotated, the roller 35 is simultaneously rotated at a high
rotational speed while coming in slidable contact with the inner
wall surface of the cylinder 31. Similarly, the contact portion at
which the roller 35 comes in slidable contact with the inner wall
surface of the cylinder 31 becomes a slidable portion.
Additionally, since the blade 37 rubs against the inner surface of
the through aperture 31a in the cylinder 31 due to the differential
pressure between the two divided chambers in the cylinder 31, the
contact portion at which the blade 37 contacts the cylinder 31
becomes a slidable portion. Further, since the right-hand end of
the blade 37 is squeezed against the roller 35 by the resilient
force of the spring 39, the contact portion at which the blade 37
comes in slidable contact with the outer surface of the roller 35
becomes another slidable portion.
With respect to the compressor constructed in accordance with the
embodiment of the present invention in the above-described manner,
each of the aforementioned slidable portions is constituted by the
combination of a first slidable member made of a cast iron having a
Vickers hardness within the range of 200 to 300 and a second
slidable member made of a carbon steel having a Vickers hardness
within the range of 200 to 300 and an average number of crystalline
grains per 1 mm.sup.2 within the range of 2000 to 3200. For
example, the shaft 21 is constituted by the first slidable member,
and the frame 27 and the subbearing 29 are constituted by the
second slidable member, respectively. In addition, the cylinder 31
is constituted by the first slidable member, and the roller 35 is
constituted by the second slidable member.
Conditions associated with the first slidable member and the second
slidable member are defined in the following manner. When the first
slidable member, i.e., the cast iron has a Vickers hardness less
than 200, it has an insufficient mechanical strength. When it has a
Vickers hardness in excess of 300, the wear loss of the first
slidable member greatly increases.
The carbon steel serving as the slidable member opposed to the
first slidable member, i.e., the second slidable member, has a
Vickers hardness within the range of 200 to 300 and an average
number of crystalline grains per 1 mm.sup.2 within the range of
2000 to 3200. When the carbon steel has a Vickers hardness less
than 200, it has an insufficient mechanical strength. When it has a
Vickers hardness in excess of 300, the wear loss of the carbon
steel greatly increases. In a case where the carbon steel having a
hardness within the aforementioned range has an average number of
crystalline grains per 1 mm.sup.2 within the range of 2000 to 3200,
each of the crystalline grains in the carbon steel exhibits a
coarse structure which is enlarged in the substantially isotropic
state. This leads to the result that elasticity of the grain
structure itself increases and wear resistance of the same is
improved remarkably. In a case where the carbon steel has the
number of crystalline grains per 1 mm.sup. 2 less than 2000, each
of crystalline grains becomes excessively coarse, resulting in the
mechanical strength of the carbon steel being undesirably reduced.
When an average number of crystalline particles exceeds 3200, each
crystalline grain becomes smaller in size and exhibits a distorted
slender shape having no isotropy. This leads to the result that
some crystalline grains are peeled off from the surface of the
substrate due to heat generated during sliding movement of the
relevant components and the peeled grains damage or injure the
opposed slidable member with an enlarged wear loss.
Incidentally, it is assumed that the average number of crystalline
grains referred to throughout the specification of the present
invention represents a value which is derived from steps of
sufficiently grinding the cut plane of a slidable member taken in
the perpendicular direction relative to the direction of slidable
movement of the slidable member, etching the cut plane using a
nitric acid solution, visually counting the number of crystalline
grains by visually observing the etched surface of the cut plane
with the aid of a microscope having a magnification of 400 and
finally converting the counted number into a number per 1
mm.sup.2.
It is desirable that materials employable for the first slidable
member and the second slidable member are selectively determined
such that the hardness of the first slidable member is slightly
higher than that of the second slidable member and that both
slidable members are practically used by combining them with each
other. This leads to an advantageous effect that wear resistance of
the refrigerant compressor is substantially improved by combinative
employment of both slidable members.
The reason why excellent wear resistance can be obtained by
combining the first slidable member and the second slidable member
with each other in the above-described manner will be described
below. As already mentioned above, HFC 134a and HFC 152a each have
high water solubility. Since a refrigerator oil having
compatibility to with HFC 134a and HFC 152a, e.g., a
polyether-based oil, a ployester-based oil or the like has an
intense polar group, its moisture absorbability is increased very
largely. This fact is evidenced by the table and a graph shown in
FIG. 11 and FIG. 12 respectively. If a considerably large quantity
of water is contained in the refrigerant or the refrigerator oil, a
film of lubricant on the surface of each slidable member is
decomposed and thereby corrosive wear of the slidable members is
enhanced with an accelerated speed of decomposition. It should be
added that no lubricant film is formed due to the presence of
chlorine atoms and the refrigerator oil has a low oil film
retaining force. With respect to the compressor for which the HFC
134a or the HFC 152a is used as a refrigerant and a refrigerator
oil having compatibility to these cooling mediums is employed in
the above-described manner, each of the slidable members is
subjected to severe operative conditions.
Generally, when a carbon steel is plastically worked, work hardness
appears on the carbon steel and each crystalline grain exhibits a
cold-rolled structure which elongates in the direction of working.
The carbon steel having the cold-rolled structure has a high
strength in the direction of cold-rolling but has a low strength in
the direction at a right angle relative to the direction of
cold-rolling. In addition, in view of the fact that each
crystalline grain is distorted, a residual stress remains in the
grain boundary with the result that each crystalline grain is kept
in a thermally unstable state. In other words, the residual stress
is readily released by heating and crystalline grains are easily
peeled off from the surface of the substrate. Once peeling has
occurred in this way, a part of the substrate having some
crystalline grains removed therefrom rubs against an opposed
slidable member, causing the wear loss to be enlarged. As the
slidable members slidably move in the compressor, a temperature of
each of the slidable members is elevated to in excess of
500.degree. C. due to slidable contact between the components made
of a metallic material and the grain structure of each slidable
member near to the surface of the substrate is largely affected
particularly in respect of wear resistance.
In contrast with this, the second slidable member employed for
carrying out the present invention, i.e. a carbon steel, is
metallurgically treated to have a Vickers hardness within the range
of 200 to 300 and an average number of crystalline grains per 1
mm.sup.2 within the range of 2000 to 3200. Each crystalline grain
exhibits a substantially isotropic shape and a grain size of the
crystalline grain is adequately enlarged to have a coarse grain
structure. Thus, a residual stress does not substantially remain in
the grain boundary including crystalline grains each having the
aforementioned shape, whereby the carbon steel is kept in a
thermally stable state. Additionally, elasticity of each
crystalline grain itself is increased. This makes it possible to
remarkably reduce the occurrence of peeling on the surface of the
substrate of the carbon steel.
According to the present invention, each slidable portion is
constituted by combining the second slidable member with a cast
iron adapted to exhibit a self-lubricating function in the presence
of a suitable hardness, i.e., the first slidable member. Therefore,
a magnitude of resistive force against heat generated by frictional
movement in the slidable portion is enlarged even under the severe
condition that a lubricant film of refrigerator oil fails to be
formed satisfactorily, and moreover excellent wear resistance is
obtainable. Consequently, the refrigerant compressor of the present
invention can stably be used for a long time by substantially
improving wear resistance in each slidable portion under the
aforementioned operative conditions.
A cast iron (to serve as a first slidable member) employed for
carrying out the present invention while having a Vickers hardness
within the range of 200 to 300 can be obtained by properly
adjusting the carbon content or the silicon content. This is
generally attributable to the fact that a hardness of the cast iron
varies depending on the relationship that a content of graphite is
increased and a hardness is reduced as an eutectic value Sc
represented by the following equation is enlarged more and
more.
In addition, since the hardness of the second slidable member
(carbon steel) and the form and size of each crystalline grain can
be controlled depending on heat treatment conditions after
completion of a working operation, the required hardness, form and
size can be obtained by employing a method which will be described
below.
After completion of a cold heading and cold forging the carbon
steel is annealed at a suitable temperature corresponding to a
carbon content thereof. Not only to soften the hardened carbon
steel but also to eliminate the influence derived from the cold
heading and cold forging, from the viewpoint of a grain structure,
it is required that the carbon steel be heated to an elevated
temperature at which a uniform austenite structure appears and
thereafter it is cooled gradually. In the case where dimensional
variation occurs due to the aforementioned heat treatment, a
machining operation is performed for the slidable members so as to
allow them to assume final dimensions, as desired. In addition, in
a case where heat treatment such as annealing or the like is given
to the slidable members, each of them has a hardness represented by
a Vickers hardness in excess of 300. Therefore, the crystalline
grains in the carbon steel which have been distorted by a working
operation can be corrected by heat treatment such as annealing or
the like such that each crystalline grain has a Vickers hardness
within the range of 200 to 300 and an average number of crystalline
grains per 1 mm.sup.2 within the range of 2000 to 3200 while
exhibiting a substantially isotropic shape.
While the present invention has been described above with the
respect to the hermetic refrigerant rotary compressor, it should,
of course, be understood that the present invention should not be
limited only to this. Alternatively, the present invention may
equally be applied to various types of refrigerant compressors such
as a semi-hermetic refrigerant compressor, a reciprocating-type
refrigerant compressor or the like.
Next, description will be made below with respect to a few
practical examples of the refrigerant compressor including a first
slidable member and a second slidable member in the above-described
manner as well as results derived from evaluation on the
examples.
EXAMPLE 1
First, a first slidable member was prepared by machining a cast
iron, JIS FC 25, specified by Japanese Standards Association
(hereinafter referred to simply as FC 25), having a Vickers
hardness of 280 to predetermined dimensions corresponding to a
required shaft. On the other hand, a bearing serving as an opposed
slidable member to the shaft was prepared using a carbon steel, JIS
S15C, containing carbon in a quantity of 0.13% by weight
(hereinafter referred to as S15C) by machining it to a
predetermined shape. Then, the resultant bearing was subjected to
heat treatment at an annealing temperature of 866.degree. C. As a
result, the bearing (second slidable member) made of a carbon steel
having a Vickers hardness of 236 and an average number of
crystalline grains of 2425 per 1 mm.sup.2 was obtained by the
foregoing heat treatment.
FIG. 3(a) is a microscopic photograph which shows the grain
structure of the carbon steel on the surface of a cross section cut
piece thereof. The microscopic photograph was obtained by visual
observation with the aid of a microscope having a magnification of
400. This surface is a cut surface which was derived from a cutting
performed in the direction at a right angle relative to the
direction of slidable movement of the slidable member. The average
number of crystalline grains was determined by counting the number
of crystalline grains using the microscope having a magnification
of 400 and then converting the value derived from the counting
operation into a number per 1 mm.sup.2. As is apparent from the
microscopic photograph shown in FIG. 3(a), the carbon steel
employed for this example is such that each crystalline grain has
an isotropic shape and exhibits a coarse grain structure compared
with a conventional carbon steel having a Vickers hardness in
excess of 300.
The refrigerant compressor as shown in FIG. 1 was assembled by
using the aforementioned slidable members. A polyester-based
refrigerator oil was introduced into the compressor and HFC 134a
was used as the refrigerant. Then, the compressor was operated for
500 hours. After operation of the compressor was completed, the
outer surface of the shaft was visually observed with the aid of a
scanning electron microscope. As a result, a trace of wear was
hardly recognized on the outer surface of the shaft.
Additionally, wear resistance of the shaft was evaluated with the
aid of a wear testing machine as schematically shown in FIG. 6.
This machine is constructed such that a shaft 51 is clamped between
V-shaped blocks 52 and 53, a load is set to a predetermined value
by tightening the V-shaped blocks 52 and 53 and the shaft 51 is
rotated while blowing a refrigerant toward the rotating shaft 51 so
as to examine a quantity of wear within a predetermined period of
time. In practice, a test was conducted such that the shaft 51 was
made of a cast iron FC 25, and the V-shaped blocks 52 and 53 were
made of the carbon steel which was prepared in accordance with
Example 1 and the shaft 51 was rotated at a rotational speed of 290
rpm while blowing the HFC 134a toward the shaft 51.
It was confirmed from the results derived from the test that the
shaft 51 was worn by a very small quantity of 2 mg and it had
excellent wear resistance by combinative employment of the cast
iron FC 25 having a Vickers hardness of 280 and the carbon steel
having a Vickers hardness of 236 and an average number of
crystalline grains of 2424 per 1 mm.sup.2 FIG. 3(b) is a
microscopic photograph which shows a macrostructure of the carbon
steel on the surface of a cross section cut piece thereof after
completion of the wear resistance test. A worn location is
represented by an arrow mark in the drawing. As is apparent from
this microscopic photograph, any significant difference can not be
recognized between the macrostructure of the carbon steel before
the test and the same after completion of the test.
EXAMPLE 2
A shaft having predetermined dimensions was prepared by performing
a cutting using a cast iron FC 25 having a Vickers hardness of 280.
On the other hand, a bearing having predetermined dimensions to
serve as an opposed slidable member was prepared by performing a
cutting using a carbon steel S15C (having a carbon content of 0.13%
by weight) and the resultant bearing was subjected to heat
treatment at an annealing temperature of 600.degree. C. After
completion of the heat treatment, it was found that the carbon
steel constituting the bearing had a Vickers hardness of 288 and an
average number of crystalline grains of 3154 per 1 mm.sup.2 FIG.
4(a) is a microscopic photograph which shows a macrostructure of
the carbon steel on the surface of a cross section cut piece
thereof. A magnification of the microscopic photograph and a method
of microscopically observing the macrostructure of the carbon steel
are same as those in Example 1.
A refrigerant compressor as shown in FIG. 1 was assembled by using
the aforementioned two slidable members. A polyalkylene glycol was
introduced into the compressor as a refrigerator oil. Then, the
refrigerant compressor was operated for 500 hours by using HFC 152a
as the refrigerant. After operation of the compressor was
completed, the surface of the shaft was visually observed with the
aid of a scanning electron microscope. The result derived from the
microscopic observation revealed that a trace of wear was hardly
recognized.
In addition, a wear resistance test was conducted in the same
manner as in Example 1. It was confirmed from the result derived
from the wear resistant test that a quantity of wear was a very
small value of 2.9 mg by virtue of combinative employment of the
cast iron FC 25 and the carbon steel S15C, and both slidable
members had excellent wear resistance. FIG. 4(b) is a microscopic
photograph which shows a macrostructure of the carbon steel on the
surface of a cross section cut piece thereof.
EXAMPLE 3
A shaft having predetermined dimensions was prepared by performing
a cutting using a cast iron FC 25 having a Vickers hardness of 240.
On the other hand, a bearing having predetermined dimensions to
serve as an opposed slidable member was prepared by performing a
cutting using a carbon steel S15C (having a carbon content of 0.13%
by weight). The resultant bearing was subjected to heat treatment
at an annealing temperature of 866.degree. C. After completion of
the heat treatment, it was found that the carbon steel constituting
the bearing had a Vickers hardness of 220 and an average number of
crystalline grains of 2130 per 1 mm.sup.2. The same refrigerant
compressor as that in Example 1 was assembled by using the
aforementioned two slidable members. A polyester-based oil was
introduced into the refrigerant compressor as a refrigerator oil.
Then, the refrigerant compressor was operated for 500 hours using
HFC 134a as the refrigerant. After operation of the compressor was
completed, the surface of the shaft was microscopically observed in
the same manner as in Example 1. The result derived from the
microscopic observation revealed that a trace of wear was hardly
recognized. In addition, it was found from the result derived from
an evaluation on a wear resistance test conducted for the shaft,
that the shaft was worn by a very small quantity of 1.7 mg.
EXAMPLE 4
A shaft having predetermined dimensions was prepared by performing
a cutting using a cast iron FC 25 having a Vickers hardness of 260.
On the other hand, a bearing having predetermined dimensions to
serve as an opposed slidable member was prepared by performing a
cutting operation using a carbon steel S15C (having a carbon
content of 0.13% by weight). The resultant bearing was subjected to
heat treatment at an annealing temperature of 866.degree. C. After
completion of the heat treatment, it was found that the carbon
steel constituting the bearing had a Vickers hardness of 250 and an
average number of crystalline grains of 2600 per 1 mm.sup.2. The
same refrigerant compressor as that in Example 1 was assembled by
using the aforementioned slidable members. A polyalkylene glycol
was introduced into the refrigerant compressor as a refrigerator
oil. Then, the refrigerant compressor was operated for 500 hours
using HFC 152a as refrigerant. After operation of the refrigerant
compressor was completed, the surface of the shaft was
microscopically observed in the same manner as in Example 1. The
result derived from the microscopic observation revealed that a
trace of wear was hardly recognized. In addition, it was found from
the result derived from an evaluation on a wear resistance test,
conducted for the shaft, that the shaft was worn by a very small
quantity of 2.2 mg.
COMPARATIVE EXAMPLE 1
A shaft having predetermined dimensions was prepared by performing
a cutting using a cast iron FC 25 having a Vickers hardness of 320.
On the other hand, a bearing having predetermined dimensions to
serve as an opposed slidable member was prepared by performing a
cutting using a carbon steel S15C (having a carbon content of 0.13%
by weight). No heat treatment was carried out for the bearing. It
was found that the carbon steel constituting the bearing had a
Vickers hardness of 310 and an average number of crystalline grains
of 3636 per 1 mm.sup.2. FIG. 5(a) is a microscopic photograph which
shows a macrostructure of the carbon steel on the surface of a
cross section cut piece thereof. This microscopic photograph was
obtained by carrying out visual observation with the aid of an
optical microscope having a magnification of 400 in the same manner
as in Example 1. As is apparent from this microscopic photograph,
the carbon steel having a Vickers hardness in excess of 300 and an
average number of crystalline grains per 1 mm.sup.2 in excess of
3200 has an elongated crystal form and a grain structure derived
from a rolling operation.
A refrigerant compressor having the same structure as that in
Example 1 was assembled by using the aforementioned slidable
members. A polyester-based oil was introduced into the refrigerant
compressor as a refrigerator oil. The refrigerant compressor was
operated for 500 hours using HFC 134a as the refrigerant in the
same manner as in Example 1. After operation of the refrigerant
compressor was completed, the surface of the shaft was
microscopically observed with the aid of a scanning electron
microscope. The result derived from the microscopic observation
revealed that a trace of wear caused by slidable movement of the
slidable members was recognized clearly.
In addition, a wear resistance test was conducted for the shaft
under the same conditions as those in Example 1 by operating the
wear testing machine shown in FIG. 6 so as to evaluate wear
resistance of the shaft. FIG. 5(b) is a microscopic photograph
which shows a macrostructure of the carbon steel on the surface of
a cross section cut piece thereof after completion of the wear
resistance test. As is apparent from the microscopic photograph,
the carbon steel had a Vickers hardness in excess of 300 and an
average number of crystalline grains per 1 mm.sup.2 in excess of
3200. It was found that the carbon steel was worn by a large
quantity of 50 mg with combinative employment of the aforementioned
slidable members, and moreover the refrigerant compressor can not
practically be used for a long time.
COMPARATIVE EXAMPLE 2
A shaft having predetermined dimensions was prepared by performing
a cutting using a cast iron FC 25 having a Vickers hardness of 150.
On the other hand, a bearing serving as an opposed slidable member
was prepared by performing a cutting using a carbon steel S15C
(having a carbon content of 0.13% by weight). The resultant bearing
was subjected to heat treatment at an annealing temperature of
950.degree. C. After completion of the heat treatment, it was found
that the carbon steel had a Vickers hardness of 170 and an average
number of crystalline grains of 1550 per 1 mm.sup.2.
A refrigerant compressor having the same structure as that in
Example 1 was assembled by using the aforementioned slidable
members. A polyester-based oil was introduced into the refrigerant
compressor as a refrigerator oil. Then, the refrigerant compressor
was operated for 500 hours using HFC 134a in the same manner as in
Example 1. After operation of the refrigerant compressor was
completed, it was found that each of the slidable members had a
shortage of mechanical strength because of their low hardness and
cracks were recognized on the shaft.
FIG. 7 is a graph which illustrates the results derived from the
Examples 1 to 4, and FIG. 8 is a graph which illustrates the
results derived from the Comparative Examples 1 and 2.
Specifically, FIG. 7 illustrates a relationship between a Vickers
hardness and a quantity of wear with respect to the carbon steels
employed for the Examples 1 to 4, and FIG. 8 illustrates a
relationship between the number of crystalline grains and a
quantity of wear with respect to the carbon steels employed for the
Comparative Examples 1 and 2. It is apparent from the two graphs
that a quantity of wear of each carbon steel is greatly increased
in the region where a Vickers hardness exceeds 300 and that a
quantity of wear of each carbon steel is rapidly increased in the
region where the number of crystalline grains of each carbon steel
exceeds 3200.
Consequently, the present invention makes it possible to
substantially improve wear resistance of each of the slidable
members by combining a cast iron having a Vickers hardness within
the range of 200 to 300 with a carbon steel having a Vickers
hardness within the range of 200 to 300 and an average number of
crystalline grains per 1 mm.sup.2 within the range of 2000 to 3200
to provide the slidable members. Additionally, the refrigerant
compressor can practically be used for an elongated period of time
by employing the slidable members as mentioned above.
Reference Example
Description will be made below with respect to wear resistance of
slidable members employed for a conventional refrigerant compressor
in which CFC 12 is used as the refrigerant.
To operate a refrigerating system having CFC 12 as refrigerant, a
paraffin-based oil was introduced into the refrigerant compressor
as a refrigerator oil, and an ordinary carbon steel (having a
Vickers hardness of 306) and a cast iron (having a Vickers hardness
of 278) were combinatively used to provide slidable members. Then,
the refrigerant compressor was operated for 500 hours in the same
manner as in Examples 1 to 4. After operation of the refrigerant
compressor was completed, the surface of the shaft was
microscopically observed with the aid of a microscope. It was found
from the results derived from the microscopic observation that a
trace of wear of the shaft was hardly recognized. In addition, it
was found from the results derived from an evaluation on a wear
resistance test conducted for the shaft that the shaft was worn by
a small quantity of 5 mg.
FIG. 9 is a graph which illustrates a quantity of wear of
respective slidable members to be combined with each other, with
respect to the Examples 1 to 4, the Comparative Examples 1 and 2
and the Reference Example. As is apparent from FIG. 9, as far as
the CFC 12 is used as the refrigerant, there does not arise any
problem even when slidable members each having a Vickers hardness
in excess of 300 are employed. However, when a refrigerant
containing no chlorine atom is used to be substituted for the CFC
12, wear resistance of each of the conventional slidable members is
largely degraded as described above in the Example 1. This leads to
the necessity for arranging a slidable member suitably employable
for with HFC 134a and HFC 152a each containing no chlorine atom. In
contrast with this, according to the present invention, since a
cast iron and a carbon steel are combined with each other while a
Vickers hardness, the number of crystalline grains and a crystal
form are properly controlled with respect to each of them, it
becomes possible to improve wear resistance of each slidable member
to an extent equal to the conventional refrigerating system having
the CFC 12 used as the refrigerant or to an extent much more than
the same.
While the present invention has been described above with respect
to the rotary type refrigerant compressor, it should of course be
understood that the present invention should not be limited only to
this but various changes or modifications may be made without
departure from the scope of the invention as defined by the
appended claims. For example, the present invention may equally be
applied to a reciprocating-type refrigerant compressor with
excellent wear resistance while slidable members are combined with
each other in the above-described manner.
* * * * *